Bill Tsai once laid out the math very clearly for me.
VCs can spend a few tens of millions on a chip startup and hope it pays off more than $100M at exit. Or they can invest a few single-digit millions in a Web 2.0 startup and have a shot at a billion.
Alas!

VCs aren't interested in projects that span more that 4 years, but with the complexity of semi industry at this point you hardly can find any semi start-up that can bring ROI in that time frame.
Software and apps could be quite complex too, but the turnaround time is much faster, especially with the app store infrastructure in place.

I'm still not sure, however, how companies that write software and apps manage to pull in hundreds of thousands of dollars in VC funding for what is basically slideware, while engineers with ACTUAL products have to fight for every dollar. The semi space does require more capex, but that's because it produces real things....